1. Field of the Invention
The present invention relates to a polymer nanocomposite, and in particular to a polyolefin-based nanocomposite prepared by melt kneading.
2. Description of the Related Art
Nanocomposites include dispersion phase having dimensions in the size ranging from 1 nm to 100 nm. The distribution of the nano-sized inorganic dispersion phase makes the nanocomposites exhibit molecular structure characteristics, such as reduced size of the inorganic particles in the dispersion, high aspect ratio of the inorganic particles, layered reinforced structure and enforced ionic bonding between inorganic phase and organic phase. The nanocomposites possessing the above characteristics accordingly can be fabricated into products that requires light-weight, high strength, high rigidity, high heat resistance, superior flame retardance, low moisture absorbability, and low permeability.
Commercially available polymer/clay dispersed nanocomposites are mainly based on Nylon 6. For example, UBE Industries Ltd. Japan has successfully produced Nylon 6-based nanocomposites, which can be fabricated into automobile parts, and high non-permeable packing films. Unitika Co., Ltd., has developed a Nylon 6-based nanocomposite which can be fabricated into automobile parts or be used as compounding materials of engineering plastics.
Nanocomposites based on other polymers are now attracting great attention from some plastics companies in the world. For example, nylon 6/clay nanodispersion formed by blend kneading developed by Allied-Signal Inc., U.S.A.; mamoacrylic paint and nanorubber developed by Kabushiki Kaisha Toyota Chuo Kenkyusho, Japan; nanonylon 66 engineering plastics by Showa Denko Kabushiki Kaisha, Japan; and nanoPET composites by Nanoco company, U.S.A are all under investigation for commercialization.
Polyolefin-based nanocomposites are now becoming more important, because a large amount of this kind of composites is used in various industries. For example, polypropylene-based nanocomposites have been largely used in automobile-related industries to replace conventional polypropylene composites.
However, since polyolefins, such as polypropylene, are non-polar functional polymers, the compatibility between the organic polyolefin and the inorganic dispersion phase, usually clay material, is inferior. To overcome the compatibility problem, one approach is to tropically functionalize the polyolefins by using a catalyst to produce polar functional groups, followed by melt kneading the modified polyolefin with organic clay material. One disadvantage of this approach is the use of a catalyst for the modification of the polyolefin. Another approach is to introduce a small amount of polymer into the organic layered clay material to swell the layered clay material. The swollen clay material is then blended with compatilizer, followed by blending with polyolefin in a batch reactor to obtain nanocomposite material. This approach involves a number of processing steps, and thus the economic effect is not high. There is another proposal which solves the compatibility problem by organization or organomodification treatment. For example, a layered-structure clay material may be modified with organic moieties attached thereto through ionic bonding, where the clay material is dispersed in an aqueous solution of an organic onium salt so as to cause the ion-exchange to take place. By doing so, the compatibility of the layered-structure clay material, the compatilizer and the polyolefin is improved. However, only the surface of the particles of the layered-structure clay material is modified and the dispersion of the particles of the clay materials is improved, the interlayer spacing (d-spacing) of the layered clay material is not improved and the compatibility problem is not completely solved.